This invention relates to a process for beneficiating coal, oil shale and similar carbonaceous solids that contain impurities in the form of inorganic sulfur and other ash-forming, inorganic constituents commonly referred to as mineral matter, and is particularly concerned with upgrading raw coal and oil shale by removing a substantial portion of these inorganic constituents.
Raw coal contains impurities in the form of inorganic, rock-like constituents which include, among other inorganic compounds, aluminosilicates, metal oxides, iron pyrites, other metal pyrites and small amounts of metal sulfates. Before coals or similar carbonaceous solids containing such inorganic impurities are used as fuel or as a feed to a conversion process, it is desirable to remove as much of the inorganic constituents as possible so that when the solids are burned or otherwise utilized they will have a relatively high BTU content, will generate relatively small amounts of sulfur-containing pollutants such as sulfur dioxide and hydrogen sulfide, and will leave relatively small amounts of unwanted ash and mineral residues.
Numerous physical and chemical processes have been proposed in the past for the improved beneficiation of coal and similar carbonaceous solids by either removing the mineral matter or sulfur. The physical methods normally involve crushing the coal to a relatively small size, subjecting the crushed coal to a gravimetric separation and recovering the low density material from the gravimetric separation as the beneficiated coal. The problem with this physical method is that only a portion of the inorganic materials is removed and therefore the low density fraction that is recovered still contains a significant amount of mineral matter. Many chemical treatments have been proposed for coal and similar carbonaceous material; however, these methods are all expensive and a large number of the proposed processes are only effective in removing sulfur. Since the above-mentioned conventional and proposed processes are either expensive or only remove a small portion of the mineral matter present, none of them appear to be a likely candidate for commercialization.